1. Field of the Invention
This invention relates to an exhaust gas-purifying system for internal combustion engines, and more particularly to an exhaust gas-purifying system of this kind having an adsorbing device arranged in the exhaust system of an internal combustion engine, for adsorbing unburnt components.
2. Prior Art
In the technical field of internal combustion engines, it is well known that a catalytic converter (three-way catalyst) is arranged in the exhaust system of the engine, for purifying noxious components, such as HC, CO, and NOx present in exhaust gases emitted from the engine.
On the other hand, to overcome an inconvenience resulting from the fact that the catalytic converter is not activated until it is warmed up to a temperature exceeding a predetermined value, an exhaust gas-purifying system has already been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 5-171929, which includes an adsorbing device for temporarily adsorbing unburnt components including HC, provided in the exhaust system together with the catalytic converter, thereby achieving satisfactory exhaust emission characteristics even when the catalytic converter has not been activated, e.g. when the engine is started in a cold condition.
The proposed exhaust gas-purifying system is constructed as shown in FIG. 1: HC and other unburnt components contained in exhaust gases emitted from an internal combustion engine 51 when the engine is started in a cold condition flow through a catalytic converter 52 and are guided by a changeover valve 53 to an adsorbing device 54 to be adsorbed thereby. When the temperature of an adsorbent charged in the adsorbing device 54 rises up to a predetermined value, the unburnt components are desorbed therefrom and returned via an exhaust gas return passage 55 to the engine 51, for combustion therein again.
However, the proposed exhaust gas-purifying system has a drawback that when the adsorbing device 54 ceases to normally function due to deterioration or aging thereof, the adsorbing capacity thereof is degraded below a predetermined level, adversely affecting exhaust emission characteristics of the engine, etc.